GATE 2016 EE – Question 63
A dc voltage with ripple is given by $v(t) = [100 + 10\sin(\omega t) - 5\sin(3\omega t)]$ volts. Measurements of this voltage $v(t)$, made by moving-coil and moving-iron voltmeters, show readings of $V_1$ and $V_2$ respectively. The value of $V_2 - V_1$, in volts, is ________.
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Correct answer: 0.30 to 0.33
Explanation
A moving-coil voltmeter reads the average value, so $V_1 = 100$ V. A moving-iron voltmeter reads the rms value: $V_2 = \sqrt{100^2 + \frac{10^2}{2} + \frac{5^2}{2}} = \sqrt{10062.5} = 100.31$ V. The difference is $V_2 - V_1 = 0.31$ V.